The present invention relates to hardware for lifting precast concrete panels by engagement with the heads of anchors recessed within the panels, and more particularly, to lifting hardware which includes a safety pin for preventing the unintentional disengagement of the hardware from the anchor head.
In order to facilitate the handling and transportation of precast concrete panels, the panels are cast with anchor pins having flared heads that are positioned within hemispherical recesses. Many types of lifting hardware have been developed to engage the recessed anchor heads, and such hardware typically includes a connecting member with a slot for engaging the anchor head, and a loop or lifting bail which is easily connected to the cable of a hoist by a hook or shackle.
One example of such lifting hardware is disclosed in Truitt et al. U.S. Pat. No. 4,368,914. That lifting apparatus consists of a lifting body having a forward portion, which includes a spoon-type connecting member and a bail, a release yoke which receives and is pivotally connected to a rearward portion of the lifting body, and a latch yoke pivotally connected to the rearward portion of the lifting body. The latch yoke includes a safety latch which cooperates with the connecting member to retain an anchor head within the slot of the connecting member. The release yoke receives a lanyard which is pulled to release the apparatus from the anchor head.
The lifting body rearward portion, release yoke, and latch yoke are all oriented substantially parallel to each other when the hardware is in the locked position and engages an anchor head. When the lanyard is pulled by a user, the release yoke pivots relative to the lifting body, which causes the release yoke and lifting body to assume a release position in which they are angled with respect to each other, and causes the latch yoke to pivot so that the safety latch is displaced away from the connecting member. At this time, the slot is pivoted away from the anchor head so that the lifting hardware is able to swing free of the concrete panel.
In order to prevent the inadvertent release of the lifting hardware from the concrete panel, the aforementioned device has been modified to provide the safety latch with an upwardly extending portion which is parallel to a boss on the release yoke. A safety pin is inserted through bores formed in the safety latch and base to prevent relative movement between the release yoke and safety latch. The safety pin is attached to the release lanyard so that a downward pull on the lanyard causes the safety pin to be removed from the bores prior to the lanyard becoming sufficiently taut to begin pivoting the release yoke. That device is illustrated in FIG. 1 of the drawings and is labelled "PRIOR ART".
A disadvantage with that design results from the loose dimensional tolerances of the release yoke, latch yoke, and lifting body, and the loose locational tolerances of the pivot connections between the yokes and the lifting body, which are a consequence of the typically low-cost casting and machining processes used to make the device. These loose tolerances frequently provide sufficient play between the components of that device such that the safety latch can be displaced sufficiently, when the apparatus is in the locked position, to enable the connecting member to slide away from its engagement with the anchor head. Consequently, the lifting hardware may disengage from the anchor head prior to the apparatus being pivoted to the release position.
Accordingly, there is a need for an apparatus for lifting concrete panels which includes a safety mechanism that prevents the inadvertent separation of the lifting hardware from the anchor head. Furthermore, such a safety device should not add measurably to the overall cost of the lifting apparatus and should be capable of being disengaged by a tugging action on the release lanyard by a user, so that the safety device can be disengaged by a person at a location remote from the lifting apparatus.